In this project methods have been developed which allow isolation, characterization and quantitation of adipose precursor cells non-determined and determined with varying degree of expression. Initial work has indicated a sequence of events occurring when adipose tissue is expanding by adipocyte hyperplasia. The research described in this application is intended to further clarify this problem. Specifically, a generally distributed signal system triggering adipocyte precursor cell replication ("adipogenic factor") will be determined in plasma and among plasma lipoproteins. The variation of such an activity will be examined in varying feeding states. Furthermore, local adipose tissue regulating factor(s), promoting adipose precursor cell multiplication and/or differentiation at a certain degree of filling of adipose tissue (adipocyte size) will be examined by "reconstruction" of adipose tissue in vitro from its main components isolated and characterized in this research project. Thereby influence of enlarged adipocytes or capillary endothelium on adipose precursor cell replication or determination will be studied as well as inhibition of the action of "adipogenic" plasma on precursor cell replication or determination by local adipose factors such as small fat cells. The characteristics of presently available adipose precursor cell preparations will be compared to define their exact usefulness as research tools by international collaborative work. From among obese adults and children followed from 5-10 years longitudinally patients characterized by increasing adipose hyperplasia will be examined as far as adipocyte and adipocyte precursor cell quantity and characteristics as well as regulatory factors in plasma and locally in adipose tissue. Bi-products of the main project will be followed up in collaboration with specialists by studying lipoprotein lipase binding to capillary endothelial cells, and by characterizing putative brown adipocytes in culture by electron microscopy and function.